Test strips are widely used diagnostic testing devices to detect the presence of one or more substances in a fluid test sample, and have applicability in the medical field as well as in chemical and industrial fields. Test strips are typically of an adsorbent material for receiving the test sample. The adsorbent material matrix serves as a carrier for an appropriate reagent for detecting the presence of the substance to be monitored. When the test sample is adsorbed onto the testing region, the reagent reacts with the substance in the test solution to indicate its presence. Chromogenic reagents are commonly used so that a visible change in color in the testing region of the strip resulting from the desired reaction confirms the presence of the monitored substance. The lack of a reaction by the reactant when the testing sample is within the test region indicates the absence of the substance.
While chromogenic test strips can be held at one end by the user and dipped to some degree into the test solution, or put on a try or the like and the test solution deposited on the strip such as by a dropper, such a construction and technique are subject to what can be called the chromatography effect, where the test solution migrates through capillary action through the portion of the test strip not initially wetted, and carries with it the developed color product, diluting and washing out the color effect. Particularly at low concentration levels, where small color changes are to be expected, the washout effect can render the test useless.
Accordingly, common test strip constructions attach the test strip to a backing, typically in the shape of a paddle, to allow the test strip to be more easily handled and the entire test strip to be dipped into the solution to be tested, and to provide structural support for the adsorbent material. The backing material usually comprises an impermeable, semi-rigid material that underlies the entirety of the absorbent material and typically extends past the adsorbent material to form a gripping element body for conveniently holding the test strip material. The backing material is adhesively attached to the adsorbent material.
While such prior art test strip paddle constructions are reliable at high concentration levels of the substance to be tested for, a major disadvantage of such constructions is that the presence of the backing and/or the adhesive that attaches the backing to the adsorbent material can interfere with the activity of the reagent. When using known test strips on fluid samples which contain low levels of the substance sought to be detected, interference caused by the backing and/or its adhesive can cause the test strip to show a “false negative” by failing to show a positive reaction indicating the presence of a substance. Therefore, it is desired to have a test strip construction that can avoid the potential for interaction between the test strip an its reagents and the supporting member or adhesive.
Another disadvantage of many prior test strips is that their design often prohibits a sufficient quantity of the test sample to react with the reagent for adequate testing results. When the test strip is backed, such a construction may inhibit sufficient adsorption of the test fluid, or result in uneven adsorption across the testing region. Striations may develop in the testing region, which makes it difficult to obtain a clear or consistent reading of the results.
Accordingly, it is an object of the present invention to provide an improved test strip construction of the supported type that avoids interaction between the supporting member and the testing region of the test strip.
Yet another object of the present invention is to provide an improved test strip construction that allows the testing region to be in full contact with the fluid to be tested.
It is another object of the present invention to provide a test strip that has improved accuracy, particularly for detecting substances at low concentration.
A further object of the present invention is to provide a test strip that is economical and efficient and cost effective to manufacture.